Are kveik thermophilic or thermotolerant: fermentation rates part 1
Updated: Jul 5, 2021
Kveik are a genetically distinct group of diverse domesticated Saccharomyces cerevisiae yeast used for generations in Norway for traditional Norwegian farmhouse brewing (1). These complex communities of yeast are usually family owned, handed down for generations, and non-purified. What we also know is that kveik are thermotolerant, ethanol tolerant, and flocculate well - reflecting their domestication over generations (1).
One of the main reasons kveik is becoming so "hot" in brewing is due to its ability to tolerate high temperatures (>28ºC) and produce relatively clean flavours when used in high temperature (up to 42ºC) fermentations (low fusels, POF-, low phenols, etc.) This adaptation could have been selected by Norwegian brewers over generations by pitching yeast into wort at relatively high temperatures before the wort had a chance to cool to room temperature (~20ºC).
What remains controversial is the fermentation kinetics of kveik yeasts at different temperatures. The White labs paper on kveik states that while most ale yeasts ferment optimally around 18-21ºC, that kveik yeasts ferment optimally closer to 32ºC. The MTF kveik page states that at least some kveik have a higher growth rate at 22ºC or 30ºC than at 37ºC. Generally, most sources agree that kveik ferment very fast (often finishing within 48 or 72 hours or less). On twitter, I recently saw an exchange on a thread on Lars Garshol's page about kveik: a twitter user asked Lars about speed comparisons at different temperatures between typical ale yeast and kveik (since kveik has been said to be fast regardless of temperature) and Lars replied there was no published data. I could go on with more examples but I can't find clear evidence whether some kveik grow better at room temperature (~20ºC) or at elevated temperatures (~35+ºC). So I decided to test it and ask, are kveik thermotolerant or thermophilic?
Thermotolerant would mean that kveik tolerate elevated temperatures (35-40ºC) but grow optimally at around room temperature (~20ºC). Thermophilic would mean that kveik grow optimally at elevated temperatures (35-40ºC). Thermophilic of course in a broad sense and not the strict scientific definition (optimal growth at 41ºC or above).
WARNING about fermentation speed and this article:
Speed is not everything; flavour/aroma/mouthfeel is more important and a good brewer will choose a temperature to match the style (for example, a NEIPA may benefit from high temperature kveik esters). This question is a question of kinetics, physiology, and evolution. For me, doing these experiments and pushing fermentations/yeast to the limit allows us to learn something about the yeast and their behaviour - which can inform our brewing. Fast fermentations are NOT always the best fermentations.
I used Lallemand Voss, Omega Hornindal blend, and Omega Lutra in fermentations at 22ºC and 35ºC in wort (OG ranging from 1.042 to 1.050) and measured the gravity and CER (CO2 evolution rate, see my post on CER here). The base beer was as follows:
60% Pilsner malt
38% Vienna malt
2% Munich malt
Mashed at 65ºC for 1 hour, 78ºC mashout for 1 min, batch sparge
Mash pH of 5.45-5.5 to counteract kveik pH drop
FG 1.007-1.012 (due to different attenuating properties of the 3 strains)
60 min boil
23 IBU Hallertau magnum at 60 min
Half a teaspoon wyeast nutrients at 10 min
0.7 IBU Hallertau Mittelfrueh at flameout
Chilled to 20ºC or 35ºC using immersion chiller
Aerated with a 5 micrometer stainless steel airstone (air) for 4 minutes
Lutra, Hornindal: fermented at 20ºC with ramp to 22ºC over 2 days or 35ºC with ramp to 37ºC
Voss: fermented at 20ºC with ramp up to 22ºC or 37ºC with ramp to 39ºC.
Pitching rate for Lutra and Hornindal: 1 pouch per 5 gallons (standard pitching rate).
Pitching rate for Lallemand Voss: 1 pack of dry yeast per 5 gallons (standard pitching rate).
I maintain temperature using a fridge fermentation chamber for my fermentation vessel coupled to an inkbird and heating pad. This allows temperature control of +/- 0.5ºC from 4ºC to 41ºC.
(If you haven't yet read my post on CER (CO2 evolution rate), it could be worth checking out before reading on)
Figure 1: Gravity and CER over time for 3 kveik at ~room temp and 35-37ºC
A) Voss and Hornindal reach terminal gravity earlier and also have a higher CER curve that flatlines earlier - this means that Voss and Hornindal ferment much faster at 35-37ºC than at 22ºC.
So a steeper gravity slope = faster ferment
Higher CER curve that flatlines sooner = faster ferment
B) For Lutra kveik, the gravity and CER curves at 22ºC and 35ºC look about the same. This means that Lutra ferments at the same speed at 22ºC and 35ºC.
Figure 2: Time to finish fermenting, max gravity points per minute activity (MGPPM), and max CER. Colours correspond to different temperatures.
The left panel in Figure 2 shows the time for each beer to finish fermenting.
Lower = faster fermentation.
The "time to finish" is not equivalent to when the fermentation hits expected FG, it is a more comprehensive measure that takes into account metabolic activity (assessed by CER).
(Please see the bottom of the post to see how I calculate time to finish fermenting)***
The middle panel shows the maximum (peak) instantaneous gravity drop in max gravity points per minute - MGPPM (the slope from the gravity curves in Figure 1).
Higher MGPPM = higher peak fermentation activity.
The right panel in Figure 2 shows the max CER for each fermentation. This corresponds to the highest peak in CER for each fermentation in Figure 1.
Higher CER = higher peak fermentation activity.
From Figure 2:
C) Voss is faster than Hornindal and Lutra; Voss is the fastest to finish at ~27 hours
D) Voss is much faster (42 hours faster to finish) at 37ºC than 22ºC
-Voss also has a 2-fold higher max gravity points per minute activity (MGPPM) and 1.9-fold higher max CER at 37ºC than at 22ºC.
-Voss is still no slouch at 22ºC, finishing the fermentation at ~69 hours
E) Hornindal follows the same trend as Voss: much faster to finish at 35ºC than 22ºC, much higher max activity (MGPPM) at 35ºC, and much higher max CER at 35ºC
-for the data hungry: Hornindal MGPPM is 2.3 fold higher at 35ºC than 22ºC
-for the data hungry: Hornindal max CER is 1.9 fold higher at 35ºC than 22ºC
F) Shockingly, Lutra behaves very different:
-Lutra does finish slightly faster at 35ºC (~71 hours) than at 22ºC (88 hours)
-Lutra has a higher peak activity (MGPPM) and higher max CER at 22ºC
-Lutra has 23% higher peak activity (MGPPM) at 22ºC than 35ºC
G) Lutra, looking at Figure 1 and 2, may how a slight inhibition (i.e. potential stress) at 35ºC when compared to 22ºC. I would say that Lutra performs better at 22ºC. There is no reason to pitch and ferment Lutra at 35ºC (unless your chilling setup is limited) because it may be stressed at 35ºC and it doesn't finish much faster.
-Kveik are heterogeneous in their response to temperature - some like it hot and some don't
-the oddball (Omega Lutra) is an isolate of Hornindal (which has multiple strains)...which makes me wonder about isolated VS community kveik and how this affects their physiology
-Voss and Hornindal are significantly faster (fermentation time, two different activity measures) at 35-37ºC than at 22ºC.
-Suggests they are more "thermophilic" than thermotolerant
-Voss performs admirably at 22ºC - finishing the fermentation (OG 1.050) in ~69 hours
-Lutra tolerates high temps (35ºC) but prefers 22ºC (stress may be apparent at 35ºC)***
-Fermentations do not finish much faster at 35ºC***
-***(May 27th 2021 Update: this turns out to be incorrect with further testing - please see my new post on Lutra kveik here)***
-Lutra may be more thermotolerant and NOT "thermophilic"
-Lutra is better fermented cool (22ºC)
(Part 2, comparing kveik to "typical" ale yeasts at different temps is here).
Tasting notes (yeast focused):
Lallemand Voss at 37ºC: very noticeable citrus and orange peel but not overwhelming. Slight acidity.
Lallemand Voss at 22ºC: Surprisingly clean and subtle. Orange/citrus not perceptible to me. Fruity aroma but almost no fruit flavour. I got acid and a slight bitterness in terms of yeast flavour. Overall, there just aren't enough fruity esters to make this koelsch-like grist work. Malt character is a bit stripped.
Omega Hornindal at 35ºC: Strong tropical, ripe fruit. The mouthfeel is much better than Voss (at 35ºC or 22ºC). The yeast esters shine and aren't unpleasant - even though they do not fit the koelsch-like grist at all.
Omega Hornindal at 22ºC: Tropical fruit esters still reveal themselves but are more subtle. A perceptible sweetness and light fruitiness. Better than the Voss at 22ºC in terms of flavour and mouthfeel in this grist. Malt character comes out more than Voss at 22ºC.
Omega Lutra at 35ºC: Strong lemony-dough flavour dominates the palette and flavour. A couple days after kegging, this just wan't a pleasant beer and the yeast character was too strong. 10 days post kegging, the lemony-dough character faded a bit but still dominated the flavor.
Omega Lutra at 22ºC: Started off just as lemony-dough as at 35ºC, but about a week after kegging this character almost completely faded and what remained was a relatively crispy, crushable, and balanced beer. Slight esters remained in the flavour but were much more pleasant than at 35ºC. This beer fermented at 22ºC is just so much better. I can see why people would want to try pseudo-pilsners with this yeast (at this temperature) but it just doesn't have the same character as a lager (i.e. when compared to saflager w-34/70).
Overall, in the koelsch-like grist, the Hornindal at 22ºC let the malt shine the most and had the best mouthfeel. The Lutra at 22ºC was the crispest.
***How I calculate time to finish fermenting:
***(We need an objective ruler for how fast it takes a fermentation to finish, it can't simply be when I feel like the beer is done.. So how do I calculate time to finish fermenting? To calculate this cutoff, I looked at 23 different beer fermentations where I tracked the gravity and CER and calculated the median CER value at which the gravity was stable for at least 12 hours. This CER threshold value (0.00009 mol CO2/min) became the cutoff for when a fermentation is finished. Since the CER value is the cutoff, and not the gravity, sometimes the CER cutoff is reached earlier/later than 12 hours post stable gravity.)
1) Preiss, R., Tyrawa, C., Krogerus, K., Garshol, L. M. & van der Merwe, G. Traditional Norwegian Kveik Are a Genetically Distinct Group of Domesticated Saccharomyces cerevisiae Brewing Yeasts. Front. Microbiol.9, 5412 (2018).